Thermochemistry Chapter 17

TWO Trends in Nature Order  Disorder (Entropy)    High energy  Low energy (Enthalpy)  -> 

Energy & Chemistry ENERGY is the capacity to do work or transfer heat. HEAT is the form of energy that flows between 2 objects because of their difference in temperature. Other forms of energy — light electrical kinetic and potential

Potential & Kinetic Energy Potential energy — energy a motionless body has by virtue of its position.

Potential & Kinetic Energy Kinetic energy — energy of motion

Heat transfers until thermal equilibrium is established. Thermodynamics Thermodynamics is the science of heat (energy) transfer. Heat energy is associated with molecular motions. Heat transfers until thermal equilibrium is established.

Directionality of Heat Transfer Heat always transfer from hotter object to cooler one. EXOthermic: heat transfers from SYSTEM to SURROUNDINGS. Heat(system) goes down Heat(surr) goes up

Directionality of Heat Transfer Heat always transfer from hotter object to cooler one. ENDOthermic: heat transfers from SURROUNDINGS to the SYSTEM. Heat(system) goes up Heat (surr) goes down

Energy & Chemistry All of thermodynamics depends on the law of CONSERVATION OF ENERGY. The total energy is unchanged in a chemical reaction. If PE of products is less than reactants, the difference must be released as KE.

Energy Change in Chemical Processes PE of system dropped. KE increased. Therefore, you often feel a temperature increase.

UNITS OF ENERGY 1 calorie = heat required to raise temp. of 1.00 g of H2O by 1.0 oC. 1000 cal = 1 kilocalorie = 1 kcal 1 kcal = 1 Calorie (a food “calorie”) But we use the unit called the JOULE 1 cal = 4.184 joules James Joule 1818-1889

HEAT CAPACITY The heat required to raise an object’s temperature by 1 ˚C. Which has the larger heat capacity?

Specific Heat Capacity Specific Heat Capacity (or specific heat ) is the amount of heat it takes to raise the temperature of 1g of the substance 10C

Calculating Specific Heat Specific heat= heat (J or cal) mass (g) x change in temperature Add : Q 3-4 on page 510

Assignment: Read pages 505-509 Copy the vocabulary terms on page 505 onto a flippy page foldable Answer the four key concept questions on page 505 and Q 1-2 on page 507 Calculating specific heat Q 3-4 on page 510